There is a TDMA (Time Division Multiple Access) system as a system for media access control (MAC). The TDMA system is access control in performing communication between a master (a master station) and a plurality of slaves (slave stations). The stations access a medium (a cable, radio, a power line, etc.) in a time division manner. The TDMA system has a characteristic in that the slaves can be efficiently accommodated.
The TDMA system is adopted on condition that communication between the master and the slaves is performed. To apply the TDMA system between apparatuses at a long distance and perform communication, the communication is possible, for example, if the apparatuses are connected by an optical fiber in which a signal is not attenuated between the master and the slaves even at a long distance. However, when the radio or the power line is used, attenuation of a signal is large compared with the optical fiber. Therefore, in a communication system in which the master and the slaves are at a long distance, the communication to which the TDMA system is applied cannot be performed unless the communication system is changed. Therefore, to perform communication at a long distance, it is necessary to relay the signal between the master and the slaves.
In general, there is a limit in the number of slaves that the master can handle. To communicate with the slaves exceeding the number, it is necessary to configure the master and the slaves in multiple stages and relay a signal. For example, an automatic meter reading system that notifies meter values of a large number of energy meters through PLC (Power Line Communication) adopts a configuration in which repeaters are used as masters to accommodate a large number of slaves that can be accommodated therein and a master for the entire system further accommodates these repeaters. The slaves notify the masters of meter values respectively through the repeaters.
On the other hand, when only limited frequency channels can be used in a wireless LAN, a PLC, or the like, a distance between nodes allocated with the same frequency is often not sufficient and interference occurs. To prevent the occurrence of the interference, Patent Literature 1 described below proposes a method of relaying a signal in the TDMA system using the same frequency.
Patent Literature 1 proposes a relay method for preventing, even if a single frequency is used, interference from occurring by switching to perform among, at every TDMA frame time, a master operation in which a repeaters operate as master stations, a slave operation, and a pause operation in which the repeaters operate as slave stations. For example, in unit of three frame times of a frame of the TDMA, a master, a repeater A, and a repeater B connected to the repeater A apply, in order, the operation of the master station to slaves accommodated therein. Patent Literature 1 proposes a system in which the master and the repeaters operate in order in this way, whereby the master and the repeaters can communicate with each other without interfering even at the same frequency.
Patent Literature 1 also proposes a method of causing, rather than causing TDMA systems (master-slave systems including masters and repeating apparatuses or repeating apparatuses and slaves) to operate once equally for each of apparatuses, a specific TDMA system to operate a plurality of times in an entire operating period to increase an operation frequency of the TDMA system and improve throughput of the apparatuses in the system. Further, Patent Literature 1 also proposes a method of notifying an operation table describing operating times from a top master to subordinate repeaters and slaves to dynamically change the operating times.